1. Field of Invention
This invention relates to clamps such as a device for clamping a memory disk to a spindle for the purpose of testing the finished disk, burnishing or polishing, etc.
2. Prior Art
Each of the many kinds of clamps usually has a number of uses and the particular type of clamp embodied in this invention may be introduced by describing the use of clamps to attach a memory disk to a plate or "chuck" such as required at several stages of the manufacturing process. These stages include test procedures, such as measuring flatness or detecting recording errors, and manufacturing procedures such as burnishing or polishing. For these purposes, the disk is clamped on both sides wherein the clamping surface is an annular flat area concentric to the disk and extending from the inside diameter.
Published standards for the industry (ANSI specifications) state that the clamping force be uniformly distributed over the clamping area wherein both the area and the force are prescribed according to the size of the disk.
Accordingly, a clamp that has been adopted throughout the industry comprises a circular plate attached conentrically near the end of a spindle axis and having a shoulder around its perimeter. The disk is thereby positioned concentric to the spindle by the shoulder and is supported by the flat annular surface of the plate pressing on one side and a collar that is mounted concentrically and presses on the opposite side of the disk. In older versions of the prior art, the collar is screwed onto the end of the spindle protruding through the center of the disk but in more recent designs, force is applied automatically by pneumatic means after the operator positions the collar on top of the disk. The use of this clamping means is limited to manual operation in that the operator must remove the collar in order to remove the disk.
Another type of clamp is designed so that, after the disk is laid onto a supporting plate, fingers are made to extend over the clamping area in order to secure the disk. An inherent disadvantage of this design is that the fingers cannot cover the entire clamping area.
Still another type of chuck is the so called "bladder" chuck in which the disk is positioned by a collar onto a spindle supported plate and then air pressure is applied which causes a bladder to expand out over the clamping area of the disk. This design is amenable to automatic or robotic operation since there is no requirement to attach or remove a collar. However, this design does not provide the desired uniform pressure over the clamping area and the bladder clamps that are available commerciallly do not provide a clamping force called for in the ANSI specification. For example for a five inch disk, the clamping force specified in the ANSI specification is 250 pounds whereas the clamping force of the typical bladder chuck is about 50 pounds.
Hydraulic rams have been disclosed in which pressure may be applied by one combination of rams operative to apply one value of pressure while a different combination of rams is operative to provide another value of pressure. However these devices require hydraulic switches or valves to switch from one combination to the other.
To summarize the present state of the prior art, there is a need for a clamp that applies a uniform large force over the entire clamping area and the design of the clamp must be such as to avoid having to remove the clamp manually or by expensive robotic means.